Canva Senior Backend Engineer-Java interview questions

Initial call with recruiter followed by a Computer Science Fundamentals interview. After passing this interview, the next round consisted of 4 interviews - Programming Language Fluency, System Design, Technical Review / Communication and Strategy, and Communication & Leadership. I was subsequently informed all my other interviews went well but I did not pass the PLF interview as the interviewer said that, although my code worked fine, it was too "long and complicated". The question itself was a very collections-dependent problem and I was forced to not use anything from java.util package (including Java built-in collections), so I had to re-implement all I needed from scratch. Obviously if they didn't want "long and complicated" code they should let the candidate use the java.util package in their solution. I really do not understand what their expectations are here and found this outcome very disappointing after all the time invested in this process.